In embodiments, the invention provides apparatus for applying an electrical stimulus to a person's leg in timed relationship to leg movement during walking in order to achieve a benefit.
For example, a person who has a dropped foot is unable to lift his or her toes clear of the ground during the swing phase of walking. Such a problem is seen in people who have either a peripheral nerve lesion, as a result of trauma or disease, or an upper motor neuron lesion. It is the latter that responds to neuromuscular stimulation. Lesions of the lower motor neurons result in destruction of the neural pathway so that muscle contraction can be achieved only through direct stimulation of the muscle fibers. Functional electrical stimulation may therefore be suitable for the treatment of patients following stroke, multiple sclerosis, spinal cord injury T-12 and above, Parkinson's disease, cerebral palsy, head injury and familial or hereditary spastic paraparesis.
The first reference to functional electrical stimulation (FES) is the work by Liberson et al, “Functional electrotherapy in stimulation of the peroneal nerve synchronized with the swing phase of gait of hemiplegic patients”, Arch. Phys. Med. Rehabil. 42, 202-205 (1961). At this time electrotherapy was commonplace, but functional electrotherapy was a new concept. Liberson defined it as follows: ‘ . . . to provide the muscles with electrical stimulation so that at the very time of the stimulation the muscle contraction has a functional purpose, either in locomotion or in prehension or in other muscle activity. In other words, functional electrotherapy is a form of replacement therapy in cases where impulses coming from the central nervous system are lacking.’
Liberson used a portable stimulator to correct drop foot during walking. A train of pulses of 20-250 μtsec duration, frequency 30-100 Hz and maximum peak current 90 mA was applied through conductive rubber electrodes. The negative (active) electrode was placed over the common peroneal nerve below the knee and the large indifferent electrode either on the thigh or on the lower leg. The stimulator was worn in the pocket and a heel switch was used to trigger the stimulus during the swing phase of the gait cycle. The switch was worn within the shoe or on the foot on the affected side so that the electrical circuit was interrupted during the stance phase, when the weight was on the heel, and allowed to flow when the heel was lifted during the swing phase. Liberson was enthusiastic about the results, reporting that all the subjects experienced considerable improvement in gait. Despite improvements in the apparatus used, the basic idea of FES has remained unchanged. Sixteen papers on the topic published in the period 1960-1977 have been reviewed by J. H. Burridge et al, Reviews in Clinical Gerontology, 8, 155-161 (1998).
U.S. Pat. No. 5,643,332 (Stein) is also concerned with FES and explains that although variants of the technique have been tried and some success has been obtained, the most common appliance fitted to people with foot drop is an ankle-foot orthosis (AFO) which is a plastics brace that fits around the lower leg and holds the foot at close to a 90° angle with respect to the long axis of the leg, and which does not employ electrical stimulation. Stein gives a number of reasons why FES had not replaced the AFO, amongst which is unreliability of the foot switch. In order to overcome this problem, Stein proposes a tilt sensor for measuring the angular position of the lower leg, although he also provides a socket for a hand or foot switch for those patients who cannot use a tilt sensor as there is insufficient tilt of the lower leg. A muscle stimulator for knee stabilization, also based on a tilt switch, is disclosed in U.S. Pat. No. 4,796,631 (Grigoryev). Muscle stimulation for the treatment and prevention of venous thrombosis and pulmonary embolism is disclosed in U.S. Pat. No. 5,358,513 (Powell III).
U.S. Pat. No. 6,507,757 (Swain, the contents of which are incorporated herein by reference) is concerned with improving the reliability of the foot switch. In one aspect it discloses a functional electrical stimulator for attachment to a leg comprising:
first and second electrodes for attachment to the leg to apply an electrical stimulus;
a foot switch for sensing foot rise or foot strike, said foot switch comprising a force-sensitive resistor;
a circuit responsive to said foot switch for generating stimulation pulses; and
means forming part of said circuit for responding to changes in the resistance characteristics of said foot switch by adjusting a corresponding response threshold of said circuit.
In an embodiment the value of said force-sensitive resistor reduces from a maximum of about 20 MΩ to a minimum of about 2 kΩ when force is applied to it. The force-sensitive resistor in an embodiment has an active portion comprising an array of fingers in contact with a conductive pad so that mechanical pressure urging the pad towards the fingers reduces the resistance of the switch, the fingers being of a first conductive material e.g. a silver based material and having leads also of said first conductive material, said leads being covered by a second conductive material e.g. a carbon-based material. In an embodiment the circuit comprises potentiometer and a footswitch of variable impedance relative to loading, arranged to form a potential divider. The voltage produced at the point between the two components is measured and tracked when the circuit has been energized. A tracking algorithm is used to determine when the footswitch has been unloaded as the foot is raised from the ground and reloaded when the foot is planted back down. Provision has been made to enable this circuit to be de-energized when the stimulator is placed into sleep mode. Two-channel electrical stimulation is described in GB-A-2368018 (Swain) e.g. for the treatment of bilateral dropped foot.
Footwear with flashing lights controlled by pressure switches is known, see U.S. Pat. Nos. 5,546,681, 5,746,499 and 6,017,128 (L.A. Gear, Inc.), U.S. Pat. No. 5,903,103 (Garner) and U.S. Pat. No. 6,104,140 (Wut).